Protein misfolding and aggregation is a common thread behind many neurodegenerative diseases including Alzheimer's disease (AD), Lewy Body Dementia (LBD), and Parkinson's disease (PD) among others. While each disease has been primarily associated with aggregation of a specific protein; beta-amyloid (abeta) with AD, tau with AD and other tauopathies, alpha- synuclein (a-syn) with PD and LBD, more than one protein is likely to misfold and aggregate in brain tissue complicating diagnosis and treatment strategies. While all these proteins can form fibrillar aggregates, they can also form a variety of different smaller soluble aggregate structures as well. Studies indicate that small soluble protein aggregate forms are the relevant toxic species in the various diseases rather than the fibrillar aggregates that serve as diagnostic hallmarks. A variety of different intermediate oligomeric forms of each of these proteins can exist in vitro and in vivo, and different aggregate forms can have different toxic effects on cells, and may preferentially target different types of cells. Since cellular stress induced by misfolding and aggregation of one protein such as abeta may well lead to misfolding and aggregation of other proteins such as tau and a-syn, the presence of multiple misfolded proteins in different diseases should be expected. Therefore characterizing which aggregated protein species are correlated with different stages of each disease would greatly facilitate development of better diagnostic and treatment strategies. We have generated several well characterized reagents that specifically recognize different aggregated species of abeta and a-syn, and have demonstrated that the reagents recognize aggregated species occurring in tissue from diseased brains, but not healthy brains, and that the reagents can have disease specificity as well. Here we will develop and test similar reagents for detecting specific forms of tau that are present in AD brain tissue.